In the past, investigations showed that reaction with investment is an important source for gas porosity. The formation of sulphur dioxide leads either to spherical pores or to a dendritic surface structure, which can be mixed up with shrinkage porosity. However, experience in practice showed that there are also other sources for gas porosity. Frequent cases with severe gas porosity could not be explained by a simple reaction with investment. More detailed investigations proved that atmosphere in the melting chamber and pollution of metal (if used material is re-melted) can also play an important role. This type of porosity is affected by sometimes unexpected factors. The results of a research project give some information on this rather complicated matter.

Author: Dieter Ott